DUAL TRENCH ISOLATION METHOD AND FABRICATION METHOD OF FLASH MEMORY DEVICE USING ACTIVE AREA ETCHING METHOD

A dual trench isolation method using an active region etching process is provided to improve step coverage by eliminating a step between a memory cell array region and a peripheral region. A pad oxide layer and a first insulation material layer are formed on a semiconductor substrate(100). The first insulation material layer and the pad oxide layer are patterned, and the substrate is etched to form first and second trenches(TI-1,TI-2). An oxide layer is deposited on the substrate to fill the first and second trenches, and the surface of the substrate is planarized by a CMP process. A second insulation material layer is deposited on the substrate and is patterned to eliminate the second insulation material layer, the first insulation material layer and the pad oxide layer in a region where the second trench is formed. The active surface in a region having the second trench is etched. The second insulation material layer, the first insulation material layer and the pad oxide layer in a region where the first trench is formed are removed.